1. Field of the Invention
The present invention relates to a lubricant for a refrigerating machine, and more specifically, it relates to a lubricant for a refrigerating machine, which comprises a polyglycol having a specific structure or contains the same as a main component and which is stable in the presence of a FLON refrigerant.
2. Description of the Prior Art
As compressors for refrigerating machines using a FLON refrigerant, there have been used reciprocating, centrifugal and rotary type compressors. Particularly, in recent years, the EER (energy efficiency rate) of the compressor is heightened, and therefore the temperature in the exhaust port of this kind of compressor is high, so that thermal load to a lubricant is also large. For this reason, the stability of the lubricant under a refrigerant atmosphere is very important to maintain the performance of the lubricant itself.
Examples of the lubricant which has been heretofore used together with a FLON refrigerant include mineral oils such as a naphthene and a paraffin as well as synthetic oils such as an alkylbenzene, a poly-.alpha.-olefin and a polyglycol. However, in view of the above-mentioned high performance which is required in the refrigerating machine of late, it is considered that the stability of the lubricant at a high temperature is not always sufficient, when the aforesaid base oil is used singly. In particular, a polyglycol oil is excellent in viscosity properties and is also preferable as the lubricant for the rotary compressor because of good sealing properties at high temperatures and good flowability at low temperatures. In addition, the polyglycol oil is also excellent in solubility in HFC-134a which is expected as the replaceable refrigerant under the recent FLON regulation. However, the single use of the polyglycol oil is not reliable, since this kind of oil tends to deteriorate due to the coexisting FLON refrigerant.
On the other hand, for the purpose of improving the stability of the lubricant in the presence of the FLON refrigerant, it is known to add, to the lubricant, an epoxy compound such as a phenyl glycidyl ether, an epoxidized aliphatic acid monoester or an epoxidized vegetable oil (Japanese Patent Laid-open No. 49-97351 and Japanese Patent Publication No. 57-42119, etc.). According to the description of these publications, it is elucidated that the compound added functions to trap an acid produced by the decomposition of the refrigerant.